Apparatus for pumping wells



Nov. 19, 1957 G. E. O'NEAL APPARATUS FOR PUMPING WELLS Filed Feb. '8, 1956 INVENTOR GEORGE E. ONEAL (I ATTORNEY of lifting gas. -has built up in produced liquid. The above-mentioned :ferred embodiment a constriction smaller cross-sectional area than the minimum cross-sec- APPARATUS FOR PUMPING WELLS George E. ONeal, Tulsa, Okla., assignor to Pan American Petroleum Corporation, a corporation of Delaware Application February 8, 1956, Serial No. 564,214 8 Claims. (Cl. 103-52 This invention relates generally to a well pump. More particularly, this invention relates to an improvement in the cycling free piston pumping system described in a number of places, including U. S. Patent 1,932,497 Wellensiek and U. S. Patent 2,698,582 Vincent.

In the cycling free piston pumping system, sometimes "referred to as the ball pump, free pistons such as rubber balls are fed automatically into the upper end of. a power tubing string and driven to the bottom by injecting gas behind the free piston. At the bottom of the power tubing, the free piston is constrained to prevent the wasting the production tubing which is placed in the Well in parallel with the power tubing or after a predetermined time interval, the free piston is forced past the constraint by the injection of additional gas which bllllClS up a great differential pressure across the free piston tional area of the free piston, this minimum. cross-sectional area being about equal to the cross-sectional area of the production tubing. In that pumping apparatus, -it has been found that with rubber balls as thefree pistons, the differential pressure between the power tubing and 'the constriction varies as the age and wear of the ball vary so that the pumping system never becomes completely stabilized. That is, when the ball pop-through pressure changes, the amount of fluid lifted per cycle and not opthe gas/oil ratio change so that the pump does erate at maximum efiiciency for a long period of time.

It is, therefore, an object of this invention to provide an improved well pump. It is a further object of this inven tion to provide an improved free piston restriction at the bottom of the Well. It is still a more specificobject of this invention to provide a bottom hole free piston restriction for a cycling free piston pumping system that maintains a substantially constant pop-through diilerential pressure for the free piston. Other objects and advantages of this invention will become detailed description proceeds. In this description refer? ence will be made to the accompanying drawing which is :a cross-sectional view of the lower end of a cycling free piston pumping system.

After a predetermined amount of liquid the production tubing required to displace the ball through i apparent as the following ,1

This invention may be described briefly as an improved free piston restriction for a cycling free piston pumping system, the free piston being restrained by a mechanical jsnap-action means-whichpermitsi the free piston to be displaced'through the restriction at a substantially constant diiferential pressure. For a more detailed descriprice tion, reference is now made to the accompanying drawing. A tubular U-bend 10 is connected to the bottom of a production tubing 11 which may be suspended in a well. The two are connected together as by threads 12 at the production outlet of the U-bend so that the U-bend may be lowered into the well on the bottom of the production tubing. The other end of the U-bend, the lifting fluid inlet 13, may be connected toa power gas conduit 14. In one embodiment the power gas conduit and the production tubing mayboth be fixed to the U-bend and lowered into the well together as shown in the above-mentioned Vincent patent. Alternatively, the U-bend may be lowered into the well on the production tubing and the power gas conduit may be lowered into position. subsequently. In this embodiment, the embodiment illustrated, the U-bend and power gas conduit may be provided with an O ring slip joint 15 to provide a fluid-sealed remotely coupled joint between the power gas conduit and the U-bend. It will also be apparent that the power gas conduit is not required in some instances, as shown, for example, in copending application 5. N. 468,033, now Patent No. 2,755,742 in the name, of Renic P. Vincent. In that embodiment, the free piston 16 is dropped into the well in the annular space surrounding the production tubing, caught at the bottom by the funnel 17 and thereby directed into the U-bend inlet 13. In any case, the free piston 16 is restrained in the U-bend inlet by a snap-action mechanism which controls the difierential pressure between the power gas conduit and production tubing at which the free piston is displaced through the U-bend and into the production tubing. This restraining mechanism may be integral with the U-bend, but, in the preferred embodiment, it includes a housing 18 which may be either dropped into position in the U-bend extension 19 or run in on a wire line. The housing has an upper guide member 20 through which the free piston stop 21 reciprocates. This free piston stop is aligned and constrained both axially and rotatably by a set screw 22 fixed in upper guide member 20 and extending into a groove 23 in the stop. The stop is urged to its uppermost position, as shown by compression spring 24. In this position it restrains the free piston within the throat 25. This spring is in compression between the bottom end 26 of the housing 18 and the lower end of the stop 21. The stop has a shoulder 27 near the lower end against which the snap-action roller 28 is held by spring 29. This spring is connected in tension between an anchor 31 in the upper endof the housing and an arm 32 on which the roller rotates vertically about a fulcrum 33 which is also connected to the housing. The upper end of the stop may have a head 34. It also may be drilled, as indicated in the dotted outline 35, to permit an internal fishing tool to be attached so that the complete snap-action mechanism may be removed from the U-bend and the well without pulling the tubing.

The throat 25 is preferably smaller in cross-sectional area than the cross-sectional area of the production tubing and the power gas conduit and also smaller than the minimum cross-sectional area of the free pistons used. Typically, the power gas conduit and the production tubing have about the same diameter and cross-sectional area. When a tree piston is first installed, it generally has about the same diameter and cross-sectional area. Continuous use of rubber balls as free pistons tends to wear these balls so that they do not fit closely in either conduit. Consequently, even though a close fit is not required in the tubing strings, in order that the balls may be used for a long time in the system, it is generally desirable to constrict the inlet to the U- bend so that a worn ball will provide a fluid seal. The constriction may be provided either in the U-bend itself, as above described, or, alternatively, the housing 18 may be extended into and sealed to the U-bend inlet to provide a removable constriction. The amount of constriction is not particularly critical but a cross-sectional area from about 5 to about 25 percent smaller than the cross-sectional area of the production tubing is considered desirable.

The U-bend has a production inlet below the liquid level in a well. This may be provided by leaving the U-bend power gas inlet 13 open, as above described. In the illustrated embodiment, the U-bend has a production inlet 36 on the lower side which is preferably coaxial with the production tubing 11. This inlet may be substantially extended and may include a tubing packer. A standing valve 37 in a cage 38 may be lowered into this production inlet and seated on the tapered shoulder 39. A fishing neck 41 is provided on the standing valve cage so that a fishing tool can be lowered through the production tubing to remove the standing valve, if desired.

In operation, the U-bend, standing valve and snapaction restraining mechanism are placed in position in a well. The power gas conduit is then seated in the U-bend inlet. The free piston restraining mechanism and standing valve may alternatively be dropped into the power gas conduit or tubing and the production tubing respectively or they may be lowered thereinto on a wire line after the tubing is run. After all of this well equipment is in place, free pistons are injected one at a time into the upper end of the power gas conduit or into the annular space in accordance with the process described in the above-mentioned copending application S. N. 468,033. Gas is injected behind each free piston, driving it to the bottom. At the bottom of the well, the free piston is caught in the U-bend inlet and held in throat 25 by stop 21. Fluid production from the well then enters the pumping system through the production inlet and standing valve 37. After a predetermined time interval, another free piston and additional gas are injected into the upper end of the power gas conduit. The injection of additional gas builds up a high differential pressure across the free piston stationed in the throat and eventually the differential pressure across the fluid seal is great enough to displace the stop 21 downwardly against the force of springs 24 and 29. Before the free piston emerges from the throat 25, the snap-action roller 28 which is rotating about fulcrum 33 rides up over shoulder 27 reducing the force required to lower the stop. With this reduction in force, the free piston and stop are accelerated downwardly until the head 34 is in the position 34 indicated in dotted outline. This permits the free piston to pass through the U-bend inlet and throat and pass through the tubular U-bend as shown in dotted outline 16', and thence into the production tubing 11. After the free piston 16 has passed into position 16, spring 24 returns rod 21 to the original position. At the same time, roller 27 is likewise returned to the original position by spring 29 in readiness to stop the next free piston. Gas in the power conduit passes either around or through perforations in the head 34 until the next free piston arrives and is stopped by the restriction. The pressure of the gas behind the free piston being substantially greater than the bottom hole pressure in the production tubing due to the hydrostatic head of produced liquid, the slug of liquid and the free piston are displaced up the production tubing to the surface. Due to the greater pressure in the production tubing after the ball passes through the U-bend, the standing valve 37 is closed until the pressure in the tubing decreases to less than bottom hole well pressure. At the surface the production and the free piston are separated, the production going to storage and the free piston being retained in a hopper for reinjection into the power gas conduit.

The invention has been described by reference to specific and preferred embodiments. It will be apparent, however, that many modifications can be made without departing from the spirit of the invention. For example,

while in the preferred embodiment the free piston restriction has been actuated by the diflerential pressure between the power gas conduit and the production tubing, it can be seen that other means of actuation, such as a bottom hole timing mechanism or a surface-actuated electrical mechanism, can be substituted for the diiferential pressure-actuated device. Accordingly, this invention should be construed not to be limited to the embodiment herein described but should be limited only by the scope of the appended claims.

I claim:

1. A free piston restriction for a cycling free piston pumping system comprising a tubular U-bend having a lifting fluid inlet and a production outlet substantially in parallel, a production inlet to said U-bend, said lifting fluid inlet being adapted to form a fluid seal with a free piston, resilient means to position said free piston in said lifting fluid inlet, and snap-action means between said U-bend and said resilient means to release said resilient means upon application of a predetermined force to permit said free piston to pass through said lifting fluid inlet and into said production outlet.

2. A free piston restriction for a cycling free piston pumping system comprising a tubular U-bend having at one end a lifting fluid inlet and at the other end a production outlet, a production inlet to said U-bend substantially coaxial with said production outlet, a throat in said lifting fluid inlet adapted to form a fluid seal with a free piston, resilient means to position a free piston in said throat, and snap-action means between said U-bend and said resilient means initially to restrain said free piston in said throat and finally to release said resilient means upon the application of a predetermined force and permit a free piston to pass through said throat and into said production outlet.

3. A free piston restriction for a cycling free piston pumping system comprising a tubular U-bend having a lifting fluid inlet and a production outlet substantially in parallel, a production inlet to said U-bend, said lifting fluid inlet being adapted to form a fluid seal with a free piston, a stop initially to restrain a free piston in said lifting fluid inlet, snap-action means between said U-bend and said stop to release said stop under a predetermined condition and permit a free piston to pass through said lifting fluid inlet and into said production outlet, and means to return said stop to its initial position.

4. A free piston restriction according to claim 3 including a standing valve in said production inlet.

5. A free piston restriction according to claim 4 ineluding means to remove said standing valve through said production outlet.

6. A. free piston restriction according to claim 3 ineluding means to remove said stop through said lifting 7. A free piston restriction according to claim 3 including a throat within said fluid inlet, said throat being substantially smaller than a free piston.

8. In a cycling free piston pumping system including a lifting fluid conduit, a production tubing, a tubular U-bend connecting said conduit and said tubing, at least one cycling free piston, and a free piston constraint in said lifting fluid conduit, the improvement in said constraint comprising a stop initially to restrain said free piston in said constraint, snap-action means between said U-bend and said stop to release said stop under a predetermined force and permit said free piston to pass through said constraint and into said production tubing, and means to return said stop to its initial position.

Wellensiek Oct. 31, 1933, Vincent Jan. 4, 1955 

